Is 8 mpg normal on a 79 Corvette
07-03-2016, 01:53 PM
#21
Racer
My 79 has a test pipe with stock exhaust, Pertronix HEI upgrade (Hotter coil, adj. advance and curve), Taylor wires, Platinum plugs (use Autolite). Get some one who knows how to rebuild and tune Q-JET. My speedo is off a bit after correcting for error I came out with 15-16 MPG. When I got the car I was lucky to get 10 MPG. Also change springs on the linkage soo the secondary's kicked in sooner. Had the work done at my regular garage the owner works on the classics the other guys get stuck with new stuff. He's a Ford guy be he has the touch
Last edited by hotrodnick; 07-03-2016 at 01:54 PM.
07-03-2016, 03:30 PM
#23
You need an old school mechanic like Lars that knows how to rebuild a qjet and setup up the distributor correctly. Not many folks left that can do that.
I owned 79 l82 almost new in 1980 . It got 11-14 mpg , maybe 15 at 55 mph on level road. With 3:70 rear m21 cr.
Before that I owned a 1978 bone stock L48 350 auto with 3:08 rear ....this was 1979 . It ran really nice . Grocery getter. AC worked great ! Nice car.
On my 250 mile trips to college .....I averaged about 17-19 mpg .....on level non mountainous roads at 55mph ......that was national speed limit . I obeyed it ......easy way to be corvette less really fast . Police seemed very intollerant compared to today where people ignore the highway signs entirely.
The L 48 ran sweet .....never over heated.......low rpm at 55 mph . Decent gas mileage.
Problem today is the high speeds everywhere. It's 70 mph ....with most idiots driving 80-100 .
Cars of the 60-70 's other than few big boats , we're just not comfortable running 80 on the interstates . They were not gear to comfortable run 80 mph all day . There were no over drives ......few five speed any things . Caddys could cruise all day at 100 . Most everyday cars were not setup for long sustained trips at 75 mph.
Actually my 454 74 is pretty good with 3:36 CR setup , I get 11-14 mpg if I drive calmly. I can run 75 and not feel like the car is going to blow up.
. And it has the power to stay with most of the newer cars normal driving .
My old Ford truck was not designed for driving over 60-65 mph . I get run over......by 300hp mini vans with race suspensions
I owned 79 l82 almost new in 1980 . It got 11-14 mpg , maybe 15 at 55 mph on level road. With 3:70 rear m21 cr.
Before that I owned a 1978 bone stock L48 350 auto with 3:08 rear ....this was 1979 . It ran really nice . Grocery getter. AC worked great ! Nice car.
On my 250 mile trips to college .....I averaged about 17-19 mpg .....on level non mountainous roads at 55mph ......that was national speed limit . I obeyed it ......easy way to be corvette less really fast . Police seemed very intollerant compared to today where people ignore the highway signs entirely.
The L 48 ran sweet .....never over heated.......low rpm at 55 mph . Decent gas mileage.
Problem today is the high speeds everywhere. It's 70 mph ....with most idiots driving 80-100 .
Cars of the 60-70 's other than few big boats , we're just not comfortable running 80 on the interstates . They were not gear to comfortable run 80 mph all day . There were no over drives ......few five speed any things . Caddys could cruise all day at 100 . Most everyday cars were not setup for long sustained trips at 75 mph.
Actually my 454 74 is pretty good with 3:36 CR setup , I get 11-14 mpg if I drive calmly. I can run 75 and not feel like the car is going to blow up.
. And it has the power to stay with most of the newer cars normal driving . My old Ford truck was not designed for driving over 60-65 mph . I get run over......by 300hp mini vans with race suspensions
Last edited by LS4 PILOT; 07-03-2016 at 03:38 PM.
07-04-2016, 10:38 AM
#24
thought i'd dig up this old thread, as i found out something interesting this morning. guess i should leave the car stock and stop foolin' around. 
1979 L48 auto that's bone stock except for true duals. has factory spoilers said to increase MPG by one or two. she starts easy, runs great, fresh plugs, fuel filters, etc. i use a container of Techron a few times over the summer to keep the fuel system clean, and seems to work so far.
i had previously removed the intake plenum and associated tubes in order to clean up the engine compartment, this was done last year i think. checking mileage the other day i traveled 39.1 miles, mainly highway with a bit of in town, using 3.02 gallons. 13 MPG
remembering that the plenum was supposed to increase efficiency a bit, i reinstalled the assembly and traveled the same route at the same ambient temp, and was fortunate enough to use the same pump nozzle. i stopped fueling when the nozzle clicked "off" after seeing only 2 gallons used. i tried to add more but couldn't. 38.7 miles (i guess the odo off a touch) used 2.02 gallons. 19.1 MPG
i'll leave the plenum on.
1979 L48 auto that's bone stock except for true duals. has factory spoilers said to increase MPG by one or two. she starts easy, runs great, fresh plugs, fuel filters, etc. i use a container of Techron a few times over the summer to keep the fuel system clean, and seems to work so far.
i had previously removed the intake plenum and associated tubes in order to clean up the engine compartment, this was done last year i think. checking mileage the other day i traveled 39.1 miles, mainly highway with a bit of in town, using 3.02 gallons. 13 MPG
remembering that the plenum was supposed to increase efficiency a bit, i reinstalled the assembly and traveled the same route at the same ambient temp, and was fortunate enough to use the same pump nozzle. i stopped fueling when the nozzle clicked "off" after seeing only 2 gallons used. i tried to add more but couldn't. 38.7 miles (i guess the odo off a touch) used 2.02 gallons. 19.1 MPG
i'll leave the plenum on.
07-04-2016, 12:27 PM
#25
Melting Slicks
Member Since: May 2015
Location: Cape Girardeau Missouri
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I'm almost positive he's talking about the original air intake a.k.a. "cold air intake". On the '79 both the L48 and L82 engines had a stock dual snorkel cold air intake. By design the side intake only opens during wide-open throttle.
While I've said it a few times here now, it bears repeating that the later C3s that are filled with vacuum operated emission controls plus all the other vacuum operated devices and accessories often find those hoses SEVERELY neglected. They may look fine but if original or of unknown age I can almost guarantee that nearly every connection is leaking at least a bit.
The best "improvement" by far that I've made to my low mileage '79 L82 is to replace all of those vacuum hoses! Both performance and fuel economy were greatly enhanced even if the increase in performance sometimes keeps me from enjoying the increased fuel economy
Look up Doc Rebuild for hose sets. They are of excellent quality, color coded just like the originals and come with excellent hookup diagrams. Also be certain to replace all of the hoses associated with the EFE (evaporative fuel emission) system as they are likely to be in the worst condition of all.
While I've said it a few times here now, it bears repeating that the later C3s that are filled with vacuum operated emission controls plus all the other vacuum operated devices and accessories often find those hoses SEVERELY neglected. They may look fine but if original or of unknown age I can almost guarantee that nearly every connection is leaking at least a bit.
The best "improvement" by far that I've made to my low mileage '79 L82 is to replace all of those vacuum hoses! Both performance and fuel economy were greatly enhanced even if the increase in performance sometimes keeps me from enjoying the increased fuel economy
Look up Doc Rebuild for hose sets. They are of excellent quality, color coded just like the originals and come with excellent hookup diagrams. Also be certain to replace all of the hoses associated with the EFE (evaporative fuel emission) system as they are likely to be in the worst condition of all.
07-04-2016, 01:37 PM
#26
stock plenum benefits
the oval-shaped air cleaner intakes are connected to flexible tubes of accordian-like construction. these in turn are connected to the wide,flat plenum that mounts directly on top of the radiator bracket. see pic.
am still perplexed as to why the dramatic MPG increase when installing the OEM air intake system. have done a little research into the benefits of relatively cooler air supplying the carb.
concurrent with intake air now being driven into the air cleaner, the air is relatively cooler, too. both MPG tests were performed at about 80/85 ambient temp days. rather than the carb being supplied with air at engine compartment temps of maybe 145 degrees the intake air was at ambient temps.
does this make any sense? i won't kick at going from 13 to 19MPG, but am curious too. thx,
bob p
am still perplexed as to why the dramatic MPG increase when installing the OEM air intake system. have done a little research into the benefits of relatively cooler air supplying the carb.
concurrent with intake air now being driven into the air cleaner, the air is relatively cooler, too. both MPG tests were performed at about 80/85 ambient temp days. rather than the carb being supplied with air at engine compartment temps of maybe 145 degrees the intake air was at ambient temps.
does this make any sense? i won't kick at going from 13 to 19MPG, but am curious too. thx,
bob p
Last edited by standswithabeer; 07-08-2016 at 08:48 AM.
07-05-2016, 04:00 PM
#28
Racer
We put on an adapter (I think it's called a ratio right) made the speedo correct. Sure it's in the head, it's a problem with some of the old cars around here, my buddy uses GPS for his speedo.
